"This is important because previously HPV was thought to be one of the risk factors for this type of cancer along with tobacco and alcohol use, and now we know that it is the leading cause of this type of cancer," said Dr. Aimee Kreimer, a professor at the National Cancer Institute and one of the study’s authors.

Oral HPV is transmitted during oral sex and people with multiple oral sex partners are at the greatest risk for contracting the disease, said Kreimer.

Study participants who reported having more than six oral sex partners in their lifetime were 8.6 times more likely to develop the HPV-linked cancer, the study showed.

After studying 100 men and women newly diagnosed with oropharyngeal cancer, researchers found people with prior evidence of oral HPV were 32 times more likely to get throat cancer than those who do not have HPV.

Smoking increases the risk of developing throat cancer three-fold and alcohol increases the risk by about 2 ½-times.

HPV was present in the tumors of 72 percent of oropharyngeal cancer patients enrolled in the study and is believed to cause about 60 percent of oropharyngeal cancers and about a third of all oral cavity and pharynx cancers in the United States.

Kreimer said alcohol and tobacco are still considered the leading causes of cancer of the oral cavity and pharynx.

The use of alcohol and tobacco combined with the presence of HPV did not appear to increase the risk of contracting oropharyngeal cancer, according to the study.

Oropharyngeal Cancer Rare

Oropharyngeal cancer is rare and currently affects about 11,000 people nationwide. Most people who get oral HPV will not develop the disease, Kreimer said.

Still, there is currently no test available to determine whether someone has oral HPV so regular dental visits are important in the prevention of throat and related cancers, said Kreimer.

"The dentist is the first line of defense against oral cancer," she said. "The use condoms or dental dams during oral sex are always a good idea because HPV isn't the only disease that can be transmitted through oral sex. There are other STDs out there as well."

She said she and other researchers are currently studying oral HPV to better understand it.

"There's still so much we don't know about it," Kreimer said. "We're trying to characterize it and understand what it looks like and how it behaves in the oral region.

In addition to oral sex, oral HPV may also be transmitted mouth-to-mouth and can be transmitted by skin contact and in the mucus of the genital tract, and in saliva, urine, and semen, the study said.

Although the FDA has approved the vaccine Gardasil for the prevention of genital HPV infection in girls and young women, it has not been proven effective in the prevention of the oral infection, said Kreimer.

"The important thing is that we know what's causing (the cancer)," she said. "Now you can go on to learn how to screen for it and how to treat it."